A lot of videos on double knitting say to use a single stranded cast on and join the second color on the first row after the cast on or use a tubular cast on. But this means that you have 1 row where you see the same color because it isn’t until you knit the second row that you start seeing the positive and negative effect.
Couldn’t you use a double stranded long tail cast on? You would only have to cast on half as many stitches and you would already know which ones to knit and which ones to purl and would have the 2 colors on each side without 1 row where just 1 color is visible because you joined the second color after the cast on.
Is it for security reasons(getting an opening at the cast on) that I have never heard of people using a double stranded cast on? Or is it just not commonly done?